The present invention relates in general to a timer for controlling the dispensing cycle of the dispensing machine. The timer may be used in association with the dispensing of such products as instant mashed potatoes, coffee, juices, or beverages. More particularly, in accordance with this invention there is provided a timer with improved touch control.
It is desirable in accordance with the present invention to maintain current flow associated with control switches for a timer, such as one used in association with a dispensing machine, at a relatively low value, preferably less than 5 milliamperes under fault. One technique used in the prior art to alleviate problems due to switch failure, is to provide an isolation transformer to isolate the logic power supply from the line voltage. In this way the hazard of electrocution is removed even if one were to make contact with metallic portions of the touch switches. However, the cost of an isolation transformer is quite excessive, especially if it is required to carry both the power of the load as well as the logic power. In the example referred to herein, the load power includes power for a solenoid and gear motor. If the transformer supplies only the logic power, then separate means such as optical couplers are usually provided to isolate the load switches which may be triacs, from the logic. There is substantial cost involved in the use of such an isolation transformer.
One object of the present invention is to provide a timer, preferably for use in controlling a dispensing cycle associated with the dispensing machine, and which does not require the use of a transformer for power isolation.
Transformerless DC power supplies with off-line rectifiers are also well known; the AC/DC tube radio being a familiar example. The intrinsic electrocution hazard in these radios is reduced by insulating the chassis with cabinetry and control knobs which prevent the operator from making a direct contact with metal. However, with many dispensing machines, the control switches themselves cannot be relied upon solely to maintain the electrical isolation needed to prevent shock.